In known powder coating system the workpieces to be coated are moved within a coating cabin in horizontal direction past powder coating guns which are moved up and down so that the whole workpiece will be exposed to the powder. As a rule, a plurality of coating guns are arranged to succeed one another (horizontally) in the direction of passage of the workpieces. There are historical reasons for configurations which comprise several coating guns, one behind the other:
The powder coating efficiency so far was not such as to allow only one coating gun to be moved up and down and yet produce a coated workpiece. A sufficiently thick coat could be achieved only with a plurality of coating guns disposed in series behind one another.
The amount of powder discharged by a single coating gun per unit time was not sufficiently constant and satisfactory homogeneity of the powder coat consequently could be obtained only by cooperation of a plurality of coating guns arranged one behind the other.
In the meantime, a great step ahead was taken in the development of powder coating technology as regards the two points mentioned above, and nowadays coating system is built in which the coating guns are disposed in vertical orientation above each other so that, with the workpiece passing them in horizontal direction, only one coating gun each is "respon-sible" for coating a particular horizontal stripe of the workpiece. This configuration has the advantage of allowing the coating cabin to be much shorter, as will be readily apparent to those skilled in the art. In this respect reference is made also to FIGS. 1 and 2 which will be explained in greater detail below.
The arrangement of vertically aligned coating guns, however, gives rise to a new problem. If there is a variation in the amount of powder discharged from a coating gun, or if a coating gun fails altogether (e.g. due to plugging in the powder supply hose or nozzle) then a full horizontal stripe on the workpiece will be provided with too thin a coat or none at all. Moreover, this flaw cannot be made up for by subsequent coating guns, as would be the case if there were a horizontal succession of coating guns.